Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A number of scientific methods have been developed in the medical field to evaluate physiological conditions of a person by detecting and/or measuring one or more analytes in a person's blood or other bodily fluids or tissues. The one or more analytes could be any analytes that, when present in or absent from the blood, or present at a particular concentration or range of concentrations, may be indicative of a medical condition or health state of the person. The one or more analytes could include enzymes, reagents, hormones, proteins, cells or other molecules, such as carbohydrates, e.g., glucose.
In a typical scenario, a person's blood is drawn and either sent to a lab or input into a handheld testing device, such as a glucose meter, where one or more tests are performed to measure various analyte levels and parameters in the blood. For most people, the blood tests are infrequent, and an abnormal analyte level indicative of a medical condition may not be identified until the next blood test is performed. Even in the case of relatively frequent blood testing, such as may be found with those with diabetes, who regularly draw blood to test for blood glucose concentration, those blood tests are typically performed when the user is awake, although the blood glucose levels (and potential variations in such levels) occurring during the night could provide important information to assist a physician in assessing that person's medical condition. Further, most known methods of analyte detection and analysis require the collection of blood or other bodily fluid samples, which may be inconvenient, invasive and require significant patient compliance.
Moreover, some blood analytes are particularly difficult to identify and quantify with conventional sensing techniques. For small or rarified analytes, such as circulating tumor cells, for example, only one such cell may be present in 10 mL of blood. Impractically large quantities of blood would have to be drawn or otherwise sampled and analyzed in order to catch such cells with statistical significance.
Methods for analyte detection and characterization often suffer from a low signal-to-noise ratio (SNR), since the signal obtained from the analyte (in general, a small object) is typically weak in comparison to the background. This can make discerning between target analytes present in the blood, versus other analytes, particles, and tissues, etc. present in the blood and elsewhere in the body can be very difficult, especially where the measurements are taken non-invasively from outside the body. This is particularly true with some methods of analyte characterization, such as optical methods, or where the target analytes are rare in the blood or are of a relatively small size. Accordingly, such measurements can be much more time consuming (if a large volume of blood must be analyzed), less sensitive, less specific and generally less informative on the whole. For example, with fluorescence detection techniques, it is often difficult to obtain highly sensitive measurements of a target analyte because other tissues, cells, and molecules in the body may have some inherent fluorescent properties, creating a high level of background noise.